1. Field of the Invention
The present invention relates generally to the field of road navigation databases. More specifically, the present invention is directed toward a method for developing and/or progressively refining a database of road connectivity and drivability in a road network using position and/or heading information from vehicles traveling the road network.
2. Description of Related Art
Commercially available automated navigation assistance products generally utilize a computer database representing navigable roads and their interconnections in combination with software that selects one or more routes between the a starting location and a desired destination. A variety of methods may be employed to develop the database. For example, aerial photographs may be digitized and the identified roads identified by sending human observers to drive the mapped roads to assign names, etc. Most currently available methods for developing navigation databases are generally labor intensive and therefore involve substantial development costs and/or limitations in accuracy and “drivability” of the resultant database.
One example of a database of urban area roads in the United States is the Federal Government's Topologically Integrated Geographic Encoding and Referencing system (TIGER). The TIGER database was developed by the U.S. Census bureau by scanning 1:100,000 scale U.S. Geological Survey (USGS) topographic maps. A significant objective of the Census Bureau in developing the TIGER database was accurate representation of political districting boundaries. As such, while the database lacks absolute positional accuracy for many roads, the relative placement of roads represented by the database is fairly reliable. The TIGER database includes most residential and commercial roads along with their names, a representative topology, and approximate locations of address numbers. Additionally, the database is kept reasonably current, particularly in larger urban areas. Because the database is a product of the U.S. government, and thus not copyrighted, it may be used without obtaining a license or payment of royalties.
However, the TIGER database has several severe limitations that restrict, if not prevent, its utility as a “out of the box” navigation database. Specifically, absolute positional representations of roads are quite mediocre. While freeways and other major traffic arteries are represented in the database, their database locations are strongly uncorrelated with reality. This presents a problem for use with accurate position-finding equipment such as global positioning satellite (GPS) receivers—the positional fix for a vehicle on a real road may return a nonsensical “off-road” position in the database. Additionally, the database does not accurately represent fine-scale road connectivity. Grade separations, such as for example overpasses and undercrossings, are not represented—rather, TIGER typically includes these features as nodes between the two roads. Use of a database with these features for vehicle navigation would lead to nonsensical driving directions such turning from an overcrossing onto a perpendicular road whose street level is many meters below the grade of the first road. Additionally, TIGER does not include information about one way roads, restricted turns, or road blockages such as sometimes occur near railroad crossings or in residential or other restricted traffic areas. Some fictional road features, such as fragmentary, unconnected roads or roads that are erroneously represented as intersecting are also included in TIGER.
An inexpensive, less labor intensive method for developing accurate, navigable databases or, alternatively, for improving existing navigation databases is therefore desirable.